Petrogenesis and Exploration of the Earth’s Interior: Proceedings of the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 2018

This edited volume is based on the best papers accepted for presentation during the 1st Springer Conference of the Arabian Journal of Geosciences (CAJG-1), Tunisia 2018. The book is of interest to all researchers in the fields of Mineralogy, Geochemistry, Petrology and Volcanology.

The Earth's interior is a source of heat, which makes our planet unique. This source regulates the formation and evolution of rocks at larger scales, and of minerals and sediments toward smaller scales. In such context, the exploration of georesources (products) has to be related to petrogenesis (processes).

This volume offers an overview of the state-of-the-art petrogenesis and exploration in, but not limited to, the Middle East and Mediterranean regions. It gives new insights into processes and products related to the Earth's interior, and associated georesources by international researchers.

Main topics include:

1. Petrogenetic processes: geochemistry, geochronologyand geophysical approaches
2. Surficial processes: sedimentation and facies analysis
3. Applied mineralogy and tectonics
4. Geological research applied to mineral deposits

• Language: English
• Publisher: Springer
• Release date: Feb 22, 2019
• ISBN: 9783030015756

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Part IKeynote

© Springer Nature Switzerland AG 2019

D. M. Doronzo et al. (eds.)Petrogenesis and Exploration of the Earth’s InteriorAdvances in Science, Technology & InnovationIEREK Interdisciplinary Series for Sustainable Developmenthttps://doi.org/10.1007/978-3-030-01575-6_1

Biogeochemical Mapping: A New Tool to Assess the Soil Quality and Health

Pablo Higueras¹, ²  , Juan Antonio Campos¹, ³, José María Esbrí¹, ³, Eva M. García-Noguero¹, ² and Intissar Elmayel¹, ⁴

(1)

Instituto de Geología Aplicada, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain

(2)

Escuela de Ingeniería Minera e Industrial de Almadén, 13400 Almadén (Ciudad Real), Spain

(3)

Escuela Técnica Superior de Ingenieros Agrónomos de Ciudad Real, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain

(4)

Sfax University, 3029 Sfax, Tunisia

Pablo Higueras

Email: [e-mail]

Abstract

Soil health is a recently established soil-biogeochemistry related concept. It has been defined as the continued capacity of the soil to function as a vital living ecosystem that sustains plants, animals and humans. As such, it can be considered as an approach to the consideration of soil as a living being. The parameters used to assess soil health are multiple, some of which are easy and cheap to measure, while others prove to be economically costly and time-consuming, as it is the case with the genetic identification and characterization of the microbiological communities, living in a certain soil, which represent the soil biodiversity and vitality. Other parameters can be considered as approximations to this concept. In this introduction to the concept, we consider to put forward three case studies. Two of them correspond to real case studies, carried out in heavily polluted soils in relation with mining activity. As for the third study case, it corresponds to a recently funded project aimed to get a global view of the soil health relevant to the entirety of the South-Central Spain region.

Keywords

BiogeochemistrySoilEnvironmentAssessmentCase studies

1 Introduction—Concepts of Soil Quality and Health

Soil has for long been intensively affected with human activities ever since the initiation of agricultural practices. In particular, modern agriculture, highly dependent on the use of phytosanitary products for the production of intensive crops, has deeply modified the biogeochemistry of soil. Such products prove to depend highly on both of the soil’s inorganic composition, and on the biochemical activity developing on this substrate. On these bases, the soil quality concept turns out to be quite recognizable, implying the soil’s characteristics which influence its agronomic productivity. Accordingly, a modern consensus definition should be: the capacity of a soil to function, within ecosystem and land use boundaries, to sustain productivity, maintain environmental quality, and promote plant and animal health [1]. Actually, the soil health concept is rather modern, most often defined as the continued capacity of the soil to function as a vital living ecosystem that sustains plants, animals and humans [2, 3]. This implies well identifying and quantifying the temporal evolution of quality, i.e., the productivity trends, based on the generalized supposition of a decay in productivity occurring in several soils exploited for extremely long-time spans, applying soil complements, but without any heed being paid to the soil-management related effects on the soil associated microbiota.

Soil quality has been traditionally assessed by means of classical edaphological parameters, including, the soil reactivity (pH), its soluble salt contents (electric conductivity, EC), its content in organic matter (SOM), texture, structure, among several other well-known concepts and via normalized analytical procedures.

Besides, soil geochemistry, which involves the implementation of chemical analysis of major and trace elements through different analytical techniques, helps provide valuable information as to the possibilities of soil use potentials. It also provides the possibility of detecting anomalous (excessively high or excessively low) concentrations of the so-called potentially toxic elements, including the alternative denominations of heavy metals and metalloids or similar, conditioning, via the contaminated soil concept, the agronomic possibilities of such soils.

Soil biochemistry has traditionally included the application of only a few basic parameters such as the SOM and/or other related parameters, including the total or available C, N and P contents. As for modern biochemistry, however, it includes a wider range of parameters, whose initial analyses have proved to demonstrate the importance of the related systematic monitoring, whereby soil quality and health could be effectively assessed, as basically supported by the biomass biodiversity.

On this basis, soil health assessment turns out to be rather focused on integrating and optimizing the soil’s chemical, physical, and biological characters, very critical for sustained productivity and environmental quality to take place.

2 Assessment of Soil Quality and Health

As already stated, the parameters constituting the soil’s classical Edaphological parameters are very well known, and the related measurement protocols are included in a wide range of general publications, with no important novelties being put forward over the last decades.

Geochemistry, on the other hand, has been marked with a drastic change in respect of the classical analytical-chemistry based primitive methods. Indeed, the newly advanced instrumental methods, displaying lower cost and analysis time consumption benefits, including the possibility of drawing reliable results directly from the solid samples, without the need for digesting the soil and, subsequently, diluting or handling the representative samples associated contamination risks, or getting errors in the analytical process. More particularly, the application of portable X Ray Fluorescence spectrometry has provided the possibility of reaching analytical results in real time, which could, in some cases, stand as an important tool, at least in respect of the previously implemented assessment methodology, whereby soil quality could be measured in terms of major-element contents, and possible soil contaminations detected in real time.

Biogeochemistry implies the determination of new parameters involving new technologies, whose economic cost has recently been marked with a remarkable decrease, such as the PCR technology (Polymerase Chain Reaction), or other even more recent approaches useful for identifying the soil persisting microbiological communities. Yet, other technologies, of simpler application, and/or lower cost, could still be applied in the preliminary assessment procedures. Worth citing among these includes are the soil respirometry, enzymatic activity, microbial biomass, to cite but a few.

3 Case Studies

Three case studies, corresponding to the region of Castilla-La Mancha (South-Central Spain), were selected to constitute our research study set, as specified below.

3.1 Geochemical Map of the Castilla-La Mancha Agricultural Soils

Castilla-La Mancha is an extensive region sited in South-Central Spain, characterized with a low degree of industrial development, with an economy primarily based on agricultural practices, predominantly based on oil and wine production. Bravo et al. present the results of a geochemical study based on the analysis of topsoil samples, as collected from 200 soil profiles, relevant to the region based agricultural areas [4]. More specifically, it consists in a model of geochemical maps, closely similar to the general atlas [5, 6]. This study has been subject of a research project funding provided by CLM Regional government, entitled Soil biogeochemistry of Castilla-La Mancha region—Elaboration of thematic maps and setting of background- and reference levels. Accordingly, a total of 1000 additional samples of regional soils has be seleted and will be analyzed using XRF, and sequential extraction tests. The analyses will serve to stand as a recently updated geochemical data base, including the characterization of baseline and anomalous levels, along with reference values for risk assessment studies.

Besides, the project will include the recollection of 200 samples for biogeochemical analysis, including microbial biomass, soil respirometry, microbial metabolic coefficient (qCO2) and enzymatic activity.

3.2 Mercury Contamination and Dehydrogenase Activity

Almadén is a town located SW the CLM region, globally known as the source origin of almost third of total mankind produced mercury. The mining production of cinnabar (HgS), the main and almost-ore bearing elements (together with sphalerite, ZnS, usually rich in this element) had been taking place for more than 2000 years, ever since the Roman times up until 2008. The ore had been processed through pyrometallurgy to obtain the liquid metal from a number of precincts, always enclosed to avoid robbery, due to the element’s high price. One of these precincts is that sited in Almadenejos, a village within some 15 km East of Almadén, and with minor Hg ore deposits. The precinct related activity started in 1750 and ceased in 1890, and has remained closed since then. Millán et al. analyzed soil respirometry in the area lying soils, while Campos et al. studied the distribution of dehydrogenase activity in the same area [7, 8]. Both of the studies reached results proved to demonstrate that the presence of highly elevated levels of total mercury, along with its most toxic species, methylmercury, did not appear to affect the measured parameters. Notworthy, however, is that the sites with higher Hg and MeHg contents inside the precinct proved to display a practical absence of vegetal cover, highlighting the possible effect of these toxics on vegetation and, probably, on certain bacterial communities. In this respect, we consider conducting a thorough investigation of the of these toxics presence on the soil quality and health.

3.3 Decommissioned San Quintín Pb–Ag Mining Area

San Quintín constituted to act as a relatively important mine, active during the late 19th Century and the early 20th Century, for the extraction of Ag-rich galena (PbS). Together with galena, the presence of other sulphides, including pyrite and sphalerite, as well as the lack of reclamation measures after the mine and froth flotation plant, has produced an intense environmental affection in the area [9]. Zamorano et al. analyzed diverse enzymatic activities on the different scenarios actually present in the affected area, including soils with different degree of PTEs’ based contamination, old residua piles and dumps, etc. [10]. The analyses included DHA as well as the activities of β-galactosidase, acid- and alkaline phosphomonoesterase and urease. The attained results proved to reveal that the different scenarios have had null activity for certain enzymes, but normal activities for others, evidencing the presence of different bacterial communities, each living, most probably, in media supporting their specific nutrition requirements.

A similar study is being carried out by I. Mayel, from the University of Sfax, in the Trozza mine (the Kairouan region, central Tunisia), with DHA variability comparable to this found in San Quintín mine area.

4 Conclusions

The major conclusions to be retained following the conduction of this communication are mainly:

Biogeochemistry stands presently as an important tool whereby soil health could be effectively assessed, commonly recognized as the soil-to-a-living-being approach.

Biogeochemical parameters are still underway. Still, some of them can be interpreted properly in terms of microbiological health, i.e., in terms of appropriate biodiversity and vitality of the corresponding-soil persisting microbiological communities.

The soil-health related assessment processes are having, and would continue to have, an increasingly greater importance iwith respect to the environmental oriented studies.

References

1.

Doran, J.W., Coleman, D.C., Bezdicek, D.F., Stewart, B.A.: Defining Soil Quality for a Sustainable Environment. SSSA Special Publication No. 35. Soil Science Society of America, Madison, WI, USA (1994)

2.

Magdoff, F.R., van Es, H.M.: Building Soils for Better Crops: Sustainable Soil Management. Handbook Series Book 10. Sustainable Agric. Research and Education, Waldorf, MD, USA (2009)

3.

USDA: Agricultural research service northern great plains research laboratory cover crop chart (http://​www.​ars.​usda.​gov/​Main/​docs.​htm?​docid=​20323) (2014)

4.

Bravo, S., García-Ordiales, E., García-Navarro, F.J., Amorós, J.A., Pérez-de-los-Reyes, C., Jiménez-Ballesta, R., Esbrí, J.M., García-Noguero, E.M., Higueras, P.: Geochemical distribution of major and trace elements in agricultural soils of Castilla-La Mancha (Central Spain). Finding criteria for baselines and delimiting regional anomalies. Environ. Sci. Pollut. Res (in press). https://​doi.​org/​10.​1007/​s11356-017-0010-6Crossref

5.

Salminen, R., Batista, M.J., Bidovec, M., Demetriades, A., De Vivo, B., Lima, A.: Foregs—Geochemical atlas of Europe. Part 1. Background information, methodology, and maps (2005)

6.

IGME: Geochemical atlas of Spain (Atlas Geoquímico de España). Instituto Geológico y Minero de España, Madrid. In Spanish (2012)

7.

Millán, R., Schmid, Th, Sierra, M.J., Carrasco-Gil, S., Villadóniga, M., Rico, C., Ledesma, D.M.S., Puente, F.J.D.: Spatial variation of biological and pedological properties in an area affected by a metallurgical mercury plant: Almadenejos (Spain). Appl. Geochem. 26(2), 174–181 (2011)Crossref

8.

Campos, J.A., Esbrí, J.M., Madrid, M.M., Naharro, R., Peco, J., García-Noguero, E.M., Amorós, J.A., Moreno, M.M., Higueras, P.: Does mercury presence in soils promote their microbial activity? The Almadenejos case (Almadén mercury mining district, Spain). Chemosphere 201, 799–806 (2018)Crossref

9.

Rodríguez, L., Ruiz, E., Alonso-Azcárate, J., Rincón, J.: Heavy metal distribution and chemical speciation in tailings and soils around a Pb–Zn mine in Spain. J. Environ. Manag. 90(2), 1106–1116 (2009)Crossref

10.

Zamorano, P., Campos, J.A., Moreno, M.M., González-Mora, S., Peco, J.D., Higueras, P.: Mapping biological activity in soils disturbed by mining processes. In: 22nd International Conference on Environmental Indicators (ICEI2017). Helsinki, Finland (2017)

Part IIPetrogenetic Processes: Geochemistry, Geochronology and Geophysical Approaches

© Springer Nature Switzerland AG 2019

D. M. Doronzo et al. (eds.)Petrogenesis and Exploration of the Earth’s InteriorAdvances in Science, Technology & InnovationIEREK Interdisciplinary Series for Sustainable Developmenthttps://doi.org/10.1007/978-3-030-01575-6_2

Geochemical and Geophysical Evolution of Regional Mantle Flow Beneath Volcanic Harrats in the West Arabian Shield (Saudi Arabia)

Abdullah Alamri¹  , Robert Duncan², Adam Kent² and Fouzan Alfouzan³

(1)

Department of Geology and Geophysics, King Saud University, Riyadh, Saudi Arabia

(2)

College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, USA

(3)

KACST, National Center for Oil and Gas Technology, Riyadh, 11442, Saudi Arabia

Abdullah Alamri

Email: [e-mail]

Abstract

In this study, three field programs have been conducted to determine the distribution and structure of volcanic landforms (lava flows, cinder cones, eruptive centers), and collect samples for analytical studies (age determination, mineral and whole composition, isotope geochemistry). The first expedition was to Harrat Lunayyir, where recent seismic activity has indicated the possibility for developing new volcanic systems. The second expedition targeted Harrat Hutaymah, as a remarkable area for providing an extraordinary range of mantle and crustal xenoliths, which are rock fragments carried up from great depths (40–70 km) by magmas that fed lava flows and cinder cones.

Keywords

GeochemicalGeophysical evolutionRegional mantleHarratsWestern Arabian shield

1 Introduction

The Arabian Peninsula is composed of the western Arabian Shield and the eastern 45 Arabian Platform. The Shield is composed of Proterozoic island arc terranes, of a number 46, accreting together 600–900 Ma, and the basement rocks predominating the region have little to no sediment 3 47 cover. However, the Platform prevailing Proterozoic basement rocks are covered with up to 10 km of 48 Phanerozoic sediments. Several studies have shown that the upper mantle lying beneath the Arabian Shield and the Red Sea is anomalously slow, with 50 most likely associated with a shallow lithosphere-asthenosphere boundary (LAB), and 51 velocities increase towards the interior continent.

2 Materials and Methods

We reviewed previously set mapping and geologic data concerning the large Harrat Khaybar volcanic area, including the Kura, Khaybar and Ithnayn volcanic fields. The field operations were based at the Khaybar city, wherein mapping and sample collection were conducted. The suitability for future analytical work has also been assessed (age determinations, major and trace element compositions). All the existing seismic data, as provided by SGS and temporary seismic stations, have been analyzed through; (1) thin section preparation for petrographic examination of 36 samples, (2) samples’ selection for age determination purposes by means of ⁴⁰Ar-³⁹Ar incremental heating method and for the He isotope and melt inclusion studies, and (3) analysis of the major and trace element compositions through X-ray fluorescence and ICP-MS analyses. We derived new ⁴⁰Ar-³⁹Ar incremental heating-age determinants, major and trace element concentrations, and He-isotopic compositions of lava flows out of selected harrats for a better understanding of the temporal distribution of the volcanism, contribution of distinct mantle sources, along with the variable depth and melting degree across the region. We also applied the ambient noise tomography technique using data drawn from twelve seismic stations relevant to the Saudi Geological Survey, as well as from deployed portable seismic stations.

3 Results

3.1 Evaluation and Integration of Entire Datasets

The most significantly striking results achieved are the following: Volcanic activity in the transect area started with the eruption of the Kura unit alkali basalt magmas as early as 8.4 Ma. A major break in the activity occurred between 5.9 and 1.7 Ma, followed by a more or less continuous activity up to the present. The Lunayyir harrat has been active ever since 600 ka till the present, and the Hutaymah harrat from 850 ka to the present. All centers have exhibited a recent geological activity (i.e., Holocene, younger than 10 ka). However, rocks younger than about 20 ka cannot be precisely dated by the ⁴⁰Ar-³⁹Ar incremental heating method, and further resolution of age relationships among the youngest eruptions entail implementation of other methods, such as ¹⁴C. A significant outcome of our dating determination studies was the recognition of errors occurring in the previously reported K-Ar age determinations, due to mantle-derived (excess) ⁴⁰Ar predominantly characterized with xenolithic material. Hence, the activity prevaiking in Lunayyir and Hutaymah is considerably younger than previously reported.

The lava flows and cinder cones predominating the Harrats transect are predominantly of alkali basalt composition, and quite distinct from the tholeiitic basalt compositions characterizing the Red Sea floor and margins. This finding is the result of differing melting conditions (shallow and extensive under the Red Sea, deeper and less melting under the Arabian shield), and probably differing mantle source compositions (a depleted asthenosphere vs a somewhat enriched one). The rocks prevailing at Lunayyir and Hutaymah fall entirely within the alkali basalt and basanite fields, indicating little modification of magmas arising from the mantle to eruption sites occurring at the surface. At Harrat Khaybar, however, evolved compositions such as trachytes and phonolites occur, indicating that magmas have accumulated in shallow level crustal chambers, and have been fractionated due to the removal of minerals such as olivine, clinopyroxene and plagioclase. Evidence for the importance of crustal magma chambers lying at this Harrat site is also noticeable in the development of large central volcanoes.

Hence, it follows that the Harrat volcanic provinces could well be the result of a passive response to lithospheric faulting and thinning taking place around the plate edges. Active geodynamic models [1, 2] involve flow of the upper mantle into the region, emanating either from below or laterally, anomalously providing hot material for melting, lithospheric thinning by thermal erosion, and uplift due to buoyancy. As for the vertical flow, taking the form of several small mantle plumes, it is located beneath the largest volcanic systems. Northward lateral flow may well originate from the Afar region, a well-known mantle plume that burst into activity at about 32 Ma [3]. Considerable support for these asthenospheric flow models is drawn from the relevant seismic imaging [4, 5].

4 Conclusions and Recommendations

Measurements of He-isotopic compositions predominant in Harrat Khybar turn out to be remarkably homogeneous at 8.2 ± 0.1 RA (2 s, n = 3). Major, trace and rare earth element compositions are similar to the southern neighboring Harrat Rahat, indicating that primitive magmas have been formed starting from 10 to 18% partial melting of depleted peridotite at 15–40 km depth. Additionally, an intriguing trend of increased melting degrees is noticed at shallowing depths, with time (Zr/Nb and La/Yb trends), which we interpret as being an evidence for the lithosphere thinning process. Inversely, the magmas lying at the Harrat Lunayyir (100 km east of the Red Sea) appear to be formed at 65–80 km depth from 8 to 12% upper mantle partial melting. The tholeiitic magmas erupted at the level of the Red Sea spreading axis prove to derive from ~25% partial melting of upwelling depleted upper mantle, occurring within depths of 0–10 km. This regional variability characterizing mantle melting can have it explanation in the modest lithospheric extension and mantle decompression melting coupled with northward asthenospheric flow from the Afar hot spot (Fig. 1).

../images/473423_1_En_2_Chapter/473423_1_En_2_Fig1_HTML.png

Fig. 1

Cartoon cross-section going from the Red Sea to Harrat Hutaymah for two time frames, (<1 Ma and ~6 Ma). The scale is schematic to show features. The boundary layer below the base of the lithosphere contains convective stirring of enriched, delaminated lithosphere with asthenosphere beneath the Makkah-Madinah-Nafud (MMN) lineament and eastward transport in an enriched sub-lithosphere layer to the lithosphere-asthenosphere boundary (LAB) beneath Hutaymah. Geochemical data support geophysical imaging of the LAB, which shows greater thinning under the MMN-line compared with marginal harrats such as Lunayyir and Hutaymah

Seismic tomographic inversion showed low shear wave velocity within the range of 2.0–3.2 km/s. The study area is clearly resolved with the lowest westward group velocity. It is worth mentioning that the study area is located towards the northeast of the May 19, 2009 epicenter (ML = 5.4), where the area is presumably enriched with magmatic intrusions. The crust surrounding the fast intrusion is slower in process than that suggested by the broader Arabian-Shield associated scale models. The largest magnitude events, as occurring early in the swarm, are concentrated at shallow depths (~2 to 8 km) beneath northern Harrat Lunayyir, and these events are associated with the dyke intrusion. Geologically, these Harrats may host between 150 and 300 °C geothermal systems, hence its importance as a potential energy production source. The reached results imply a possibility for the existence of magmatic materials, of low shear-wave velocity beneath Harrat Khaybar, as a result of magma upwelling in the region. Overall, the competing geodynamic models prove to fall into two broad categories: passive and active. Such novel results also support the presumption of active geodynamic models. The He-isotopic compositions of some of the Khaybar and Rahat lavas (with values >10 RA) prove to indicate the implication and involvement of mantle plume material. Still, flow cannot be directly distinguished from beneath these lateral flow systems, lying north from the Afar region.

References

1.

Camp, V.E., Roobol, J.: Upwelling asthenosphere beneath Western Arabia and its regional implications. J. Geophys. Res. Solid Earth 97(B11), 15255–15271 (1992)Crossref

2.

Krienitz, M.-S., et al.: Tectonic events, continental intraplate volcanism, and mantle plume activity in Northern Arabia: constraints from geochemistry and Ar–Ar dating of Syrian Lavas. Geochem. Geophys. Geosyst. 10(4) (2009)Crossref

3.

Chang, S.-J., Van der Lee, S.: Mantle plumes and associated flow beneath Arabia and East Africa. Earth Planet. Sci. Lett. 302, 448–454 (2011). https://​doi.​org/​10.​1016/​j.​epsl.​2010.​12.​050Crossref

4.

Hansen, J., Sato, M., Ruedy, R., Lo, K., Lea, D., Medina Elizade, M.: Global temperature change. Proc. Natl. Acad. Sci. 103, 14288–14293 (2006). https://​doi.​org/​10.​1073/​pnas0606291103

5.

Hansen, J., Sato, M., Ruedy, R., Kharecha, P., Lacis, A., Miller, R., Nazarenko, L., Lo, K., Schmidt, G. A., Russell, G., Aleinov, I., Bauer, S., Baum, E., Cairns, B., Canuto, V., Chandler, M., Cheng, Y., Cohen, A., Del Genio, A., Faluvegi, G., Fleming, E., Friend, A., Hall, T., Jackman, C., Jonas, J., Kelley, M., Kiang, N.Y., Koch, D., Labow, G., Lerner, J., Menon, S., Novakov, T., Oinas, V., Perlwitz, J., Perlwitz, J., Rind, D., Romanou, A., Schmunk, R., Shindell, D., Stone, P., Sun, S., Streets, D., Tausnev, N., Thresher, D., Unger, N., Yao, M., Zhang, S.: Climate simulations for 1880–2003 with GISS modelE. Clim. Dyn. (2007). https://​doi.​org/​10.​1007/​s00382-007-0255-8Crossref

© Springer Nature Switzerland AG 2019

D. M. Doronzo et al. (eds.)Petrogenesis and Exploration of the Earth’s InteriorAdvances in Science, Technology & InnovationIEREK Interdisciplinary Series for Sustainable Developmenthttps://doi.org/10.1007/978-3-030-01575-6_3

Petrology, Geochemistry and Petrogenesis of the Sidi El Hemissi Triassic ‘Ophites’ (Souk Ahras, NE Algeria)

Rabah Laouar¹, ²  , Halima Saadia Zanouda¹, Sihem Salmi-Laouar¹, Amar Sebai³, Chrystèle Verati⁴, Salah Bouhlel⁵ and Adrian J. Boyce⁶

(1)

Département de géologie, Université Badji Mokhtar Annaba, B.P. 12, 23000 Annaba, Algeria

(2)

Laboratoire de Géodynamique, Géologie de l’Ingénieur et Planétologie, F.S.T.G.A.T., USTHB, BP. 32, Bab Ezzouar, 16111, Algiers, Algeria

(3)

Département de Génie Minier, E.N.P., B.P. 182, El Harrach, Algiers, Algeria

(4)

Laboratoire GéoAzur, Université Nice-Sophia Antipolis, Nice, France

(5)

Mineral Resources Team, LRM2E, Geology Department, Faculty of Sciences of Tunis, University Tunis El Manar, Tunis, 2092, Tunisia

(6)

Isotope Geosciences Unit, SUERC, East Kilbride, Glasgow, G75 0QU, UK

Rabah Laouar

Email: [e-mail]

Abstract

Sited in Souk-Ahras, the Sidi El Hemissi region stands as part of the Tellian Atlas, where the Triassic formation tectonically outcrops under the Tellian nappes of the Maghrebide chain. Dubbed ‘ophites’, mafic rocks, mainly gabbros and dolerites are interbedded in ~200 × 30 m lenticular body within the Triassic gypsum-rich formation. These rocks are composed of plagioclase, amphibole, pyroxene and scarce olivine crystals. Albitization represents the major alteration process, though chloritization, calcitization and epidotization of ferromagnesian minerals are also perceived. The geochemical observations prove to reveal that these mafic rocks exhibit medium- to low-Ti continental tholeiitic basalt affinity. They are enriched in LILE and LREE, as compared to HFSE and HREE, and display enriched-mid-ocean ridge basalt (E-MORB)-like incompatible element patterns in primitive mantle-normalized multi-element pattern. The weak Nb anomaly, along with the medium- to low-Ti contents, suggests possible interaction between an enriched mantle source-derived magma and lower crustal rocks. These chemical features display high similarities with those sited in the central Atlantic magmatic province (CAMP) of upper Triassic–lower Jurassic age. Hence, they turn out o be considered as highly linked to the western branch of the Alpine Tethys system, geologically and tectonically associated with the Central Atlantic Ocean opening.

Keywords

OphitesGeochemistryTholeiitesContinental flood basaltsSouk-Ahras

1 Introduction

The Triassic formation that crops out in both the Algerian Saharan and Tellian Atlas appear to display blocks and sills of exotic mafic rocks. Often labelled ‘green rocks’ or ‘ophites’, these rocks are thought to be emplaced in an extensional setting during the Triassic period [1].

A number of Triassic tholeiitic magmatic products, resembling those observed in this region, are exposed in south-western Europe and north-western Africa. This magmatic activity is believed to be related to the continental rifting, as associated with the early stages of the Pangea breakup. As a novel contribution provided by the present study, an initial attempt is made to highlight the petrological and geochemical features characterizing the Triassic ophites of the Tellian Atlas, as modeled in the Sidi El Hemissi outcrops. The results to be achieved, we reckon, would help, to our mind, elucidate the magma sources and the geodynamic context attached to their placement siting.

The Sidi El Hemissi region is part of the Medjerda chain, pertaining to the Tellian Atlas. This area is characterized with large outcrops of the Triassic formation, brought up to the surface under the effects of the Atlasic and Alpine tectonic events. Overlaid with the Tellian and Numidian nappes as well as the alloctonous Sellaoua units, such a formation is composed of chaotic evaporitic rocks of middle Muschelkalk to upper Keuper age [2].

The ophitic body is inter-bedded within a thick gypsum-bearing clay layer, displaying a lenticular form of about 200 m in length and up to 30 m in width. Overall, the rock is more or less altered and fractured, though massive lithologies with little alteration appear to be easily observable. In certain places, lava flows and brecciated rocks can also be identified. Based on local and detailed in situ field observations, granular, microgranular and microlithic textures turn out to be distinguishable. Mineral phases consist of large plagioclase laths of about 1 to 4 mm long, prismatic amphibole, orthopyroxene and clinopyroxene. Olivine is sporadically persistent along with the likely presence of rare biotite flakes. Accessory minerals are mainly opaques (oligiste), while the alteration products are sericite, saussurite, serpentine, uralite, epidote and chlorite.

2 Methods

Twenty samples were selected among the least altered lithologies for geochemical analyses. These samples were trimmed to remove regolith crust, trimmed to centimeter-size grains then sent to the ALS Minerals, in Spain, for major, trace and rare earth elements’ (REE) analysis. The entirety of the samples were crushed using a jaw crusher and pulverised by means of a low-chrome steel mill at the ALS. The major oxides were analyzed using lithium metaborate fusion digestion and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Trace elements, including rare-earth elements, were determined using lithium metaborate fusion digestion and inductively coupled plasma mass spectrometry (ICP-MS). Based on the standards and replicates relating analyses, the analytical precision turned to be generally greater than 5% for most of the major and trace elements.

3 Results

According to the different relevant discrimination diagrams, the studied ophites fall within the field of tholeiitic basalts (Fig. 1a) and liable to be classified as medium- to low-Ti tholeiites, displaying continental tholeiitic basalt affinity (Fig. 1b). The chondrite-normalized REE diagram (Fig. 2) displays a negative slope with enrichment in light REE, as compared to the heavy REE. A weak negative Eu anomaly is observed in the highly depleted samples, whereas the enriched samples show weak positive anomaly. The REE pattern also exhibits weak Pr negative and weak Nd positive anomalies.

../images/473423_1_En_3_Chapter/473423_1_En_3_Fig1_HTML.png

Fig. 1

a TiO2 versus Fe2O3t/MgO diagram of [3], and b Y/Nb versus TiO2 discrimination diagram of [4], both of them highlighting the continental tholeiitic basalt affinity (CTB) of the Sidi El Hemissi ophites

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Fig. 2

Chondrite-normalized [5] REE patterns of the Sidi El Hemissi ophites. Shaded field is for low-Ti CAMP tholeiites in West Africa [6, 7]

4 Discussion

The Sidi El Hemissi ophites appear to reveal a relatively low Zr/Nb and high Zr/Y as well as Nb/Y ratios, indicating that the source region of these rocks proves to be predominantly of enriched mantle (EM) type [8]. Similarly, the (La/Ce)N values are greater than 1, further confirming the enriched mantle origin presumption of such rocks. In the Ta/Yb versus Th/Yb diagram, the analyzed samples plot in a shifted position in respect of the mantle array (Fig. 3), clearly highlighting the possible interaction between an enriched mantle source-derived magma and a lower crustal rock source. Figure 4 highlights well that the studied samples clearly pertain to the field of enriched-mid ocean ridge basalts (E-MORB) and within-plate tholeiites.

../images/473423_1_En_3_Chapter/473423_1_En_3_Fig3_HTML.png

Fig. 3

Ta/Yb versus Th/Yb diagram indicating the position of Sidi El Hemissi ophites

../images/473423_1_En_3_Chapter/473423_1_En_3_Fig4_HTML.png

Fig. 4

Y/Nb versus Zr/Nb plot indicating the position of the Sidi El Hemissi ophites

The chemical composition of the investigated ophites proves to match well with those relating to the other late Triassic lava flows, especially those associated with the Central Atlantic Magmatic Province (CAMP). These similarities could be summed up as follows: (a) they highlight well the ophites’ tholeiitic character; (b) on the Fe2O3t/MgO versus TiO2 diagram of [3], they plot within the field of low-Ti continental flood basalts; (c) they reveal similar REE patterns with enriched LREE and LILE, as compared to HREE and HSFE; (d) they exhibit similar multi-element, primitive mantle-normalized patterns, often displaying an Nb anomaly; and (e) their geochemical features prove to confirm the persistence of a within-plate, anorogenic, tectonic type of setting. Accordingly, the Sidi El Hemissi ophites appear to reflect well a possible affinity with the CAMP. This igneous activity is commonly related to the Early Mesozoic fragmentation of the Pangea supercontinent and the subsequent opening of the Central Atlantic Ocean. Noteworthy, however, the origin of the Sidi El Hemissi ophites may well be considered to have a high association with the western branch of the Alpine Tethys system, as geologically and tectonically linked with the break-up of the Pangea and Central Atlantic Ocean opening.

5 Conclusions

The petrology and geochemistry study, as conducted in regard of the Sidi El Hemissi ophites, turn out to highlight persistent similarities with the findings documented concerning the CAMP of late Triassic–early Jurassic age, as actually cropping out on north-western Africa, south-western Europe, north-eastern and south-eastern America. Both magmas comprise low-Ti, LILE- and LREE-rich tholeiitic basalts, associated with the Early Mesozoic fragmentation of the Pangea supercontinent and, subsequently, the opening of the Central Atlantic Ocean.

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© Springer Nature Switzerland AG 2019

D. M. Doronzo et al. (eds.)Petrogenesis and Exploration of the Earth’s InteriorAdvances in Science, Technology & InnovationIEREK Interdisciplinary Series for Sustainable Developmenthttps://doi.org/10.1007/978-3-030-01575-6_4

Geochronology, Petrogenesis and Tectonic Implication of A-Type Granite from Zaranda (North-Central Nigeria)

Hafizullah Abba Ahmed¹, ², Lian-Xun Wang¹  , Chang-Qian Ma¹, Ibrahim Garba³, Musa Bala Girei¹, ⁴ and Victor Ikechukwu Vincent²

(1)

Faculty of Earth Sciences, China University of Geosciences, Wuhan, 430074, China

(2)

Department of Geology, Modibbo Adama University of Technology, Yola, Nigeria

(3)

Department of Geology, Ahmadu Bello University, Zaria, Nigeria

(4)

Department of Geology, Bayero